We propose to continue our very productive studies on Staphylococcal MSCRAMMs and their interactions with Fibrinogen (Fib) through further studies of the following three groups of MSCRAMMs. ClfA is the prototype of a family of cell wall anchored proteins that primarily targets the C-terminus of Fib /-chain. Preliminary results implicate a second site in the ClfA/Fib interaction. This site will be identified and the induced Fib conformational changes determined. This family of Fib-binding MSCRAMMs causes septic death in a mouse model after i.v. challenges with L. lactis expressing the staphylococcal proteins. Other S. aureus MSCRAMMs tested do not have this effect suggesting that this family of Fib/binding MSCRAMMs plays a key role in staphyloccal sepsis. The molecular interactions and pathways leading to the fatal outcome will be determined using a combination of mutated MSCRAMMs and specific mouse lines harboring specifically designed Fib genes. This information will not only contribute to our understanding of the molecular pathogenesis of staphylococcal sepsis, a disease with high mortality rates, but will aid in the identification of novel therapeutic targets. Bbp is closely related to SdrE and was initially identified as a cell wall anchored protein that interacts with a bone specific protein in the host, bonesialoprotein. Preliminary results generated in our lab show that this cell wall anchored protein also binds Fib with high affinity and targets a linear sequence within the 1-chain in human Fib that is close to the integrin binding RGD sequence. We will characterize this interaction in detail using structural and biochemical approaches and investigate the effects of Bbp on Fib coagulation and Fib-integrin interactions. The results of these studies will provide a base for future studies of the role of Bbp in staphylococcal diseases. Efb is a secreted staphylococcal protein that can associate with the bacterial surface. Earlier studies have shown that a structurally disorganized segment of Efb contains two high affinity Fib binding sites. This novel Fib-interaction will be characterized in detail by identifying the minimal high affinity Fib- binding Efb peptide and determining the crystal structure of a complex formed between a proteolytically generated Fib D-fragment and the Efb peptide. Preliminary results also demonstrate that Efb blocks the binding of the neutrophil integrin 1M22 to Fib, which may affect the phagocytotic function of this host defense cell. The results of these studies will define a novel type of microbe/Fib interaction and its biological consequences. PUBLIC HEALTH RELEVANCE: This project seeks to determine how a group of staphylococcal surface proteins interact with and manipulate the biology of the host protein fibrinogen. These interactions can lead to serious consequences for the host including death. A more detailed understanding of these interactions could lead to the design of new therapeutics to treat the deadly staphylococcal sepsis.